Prior art plastic modular timber-like structures are elongated and of rectangular cross-section to resemble natural wood landscaping timbers.
To install a retaining wall employing either plastic or wood types of landscape modules, the modules are placed one on top of the other by the installer until a vertical stack of the desired height is assembled. The modules are secured one to the other by fasteners, such as bolts, nails or spikes driven through the upper module into an immediately adjacent lower module positioned directly under the upper module. Plastic modules are typically formed with through-bores at spaced apart intervals along the module during the manufacture thereof, so that the bores are embodied in the modules as they are received at the site of installation and through which appropriate fasteners may be driven.
So long as any two superimposed modules are installed in the same lengths as they are manufactured with their butt ends in flush relationship; the bores of the two vertically stacked modules will be oriented in vertical co-alignment to receive a fastener driven into both bores. However, in the event one or more of the superimposed modules is shortened, the possibility that the bores will be vertical co-alignment becomes problematic and increases as the stack height increases.
Importantly, to enhance the structural integrity of a retaining wall, the modules are assembled in a multilayered stack wherein a separation or joint is created between horizontally opposing ends of the two end-abutting modules. With the modules assembled in a vertically staggered relationship, the opposing butt ends of two modules in one layer are secured together by another axially disposed module placed in an overlying or underlying relationship and spanning the butt joint. While staggering increases stack rigidity, it requires the installer to cut off a section of the module, which oftentimes results in vertical misalignment of the bores for receiving fasteners. Additionally, the installer may deploy a stack stabilizing module or so-called "dead man" which is a short section of the module laid at right angles to the vertical plane of the stack. One end of the dead-man is embedded in the soil behind the stack and the frontward end is positioned flush with the frontal surface of the stack and thereafter fastened to the upper surface of the wall module that the dead-man lays upon. Both installations require that transverse cuts be made through the module thereby altering the otherwise predetermined axial distances between one end of the module and the preformed bores.
These different assemblages therefore add difficulty to the problem of pre-positioning the bore holes in a plastic modular structure during manufacture to insure proper horizontal or vertical co-alignment with other preformed bores of other modules at the point of assembly. Advantageously, if such alignment were achievable the installer could use rebars as fasteners to hold a multiple module stacked assemblage together and to anchor the stack to the underlying strata.
Therefore, it would be an important advantage in the design of plastic timbers to be able to provide a pattern of preformed bore holes in the module which may be readily co-aligned with corresponding bore holes in other modules during the aforedescribed installations whether the module is used in its original manufactured length or is shortened to achieve, for example, a staggering between the modules or dead-man deployment.
Plastic landscaping timbers are typically made with solid cores. When the installer severs a solid cored module at right angles to its longitudinal axis to shorten the module, for example, the new butt end thusly created is similar in appearance to the original butt end. Therefore, the shortened module can be used practically everywhere throughout the stack without adversely affecting its aesthetic appearance. In this respect, the solid cored plastic module closely resembles its wood counterpart.
Solid core plastic modules require considerably more polymeric material to fabricate than modules that are wholly or partially hollow, and hence, hollow modules are desirable for their lighter weight and lower cost. However, a hollow module suffers a significant disadvantage in that the cross-section thereof is cavitated or partially hollow throughout and, therefore, a cross sectioned cut made through the module to, for example, shorten its length or to create a right angled butt end, results in a severed butt end which is hollow or otherwise cavitated but not completely solid throughout when viewed from that end. Therefore, it would be an important advantage to provide a module that does not have a completely solid core and yet can provide a solid end wall after being severed to reduce its length so that the butt end of the shortened module still closely resembles those of the original module from which it was severed.